The touch screen has become one of the most interesting and practical technological advancements in recent times. It's inventors could probably never have imagined that there would one day be a touchscreen in just about everyone's pocket, but that is the reality we are in. Touch screens are becoming so ubiquitous that some younger people are surprised when they find screens that lack the functionality. Touch screens may be everywhere, but do you know how they work?
There are many ways to make a functional touch screen, but in general, they follow a few simple principles. They all make a measurement at the point of impact and translate that measurement into some command for the attached device. One of the most common types of touch screen is the resistive touch screen. A resistive touch screen is made up of two layers of actual screen divided by a gap, empty space between them. One of the layers has a voltage applied to it while the other has sensors applied to it that can measure if and where they come into contact with a voltage. When one of these screens is touched, the two layers come into contact with one another and the voltage measurement is passed along to a controller where it is turned into a device-appropriate touch input.
Resistive touch screens will accept inputs from just about any object, as long as the touch is forceful enough. However, they have their drawbacks, mainly related to the picture they produce being blurrier than a regular screen. Capacitive touchscreens overcome some of these drawbacks, but are also more expensive than their resistive brethren.
A capacitive touch screen works by measuring changes in the screen's electrical field caused by a person's touch. Your body emits an electrical field large enough to alter the screen's electrostatic field when you touch it, allowing for the device to calculate where the touch is and transform it into an input. This just one of the many technologies working together that enable you to enjoy all those apps (as well as answer calls) on your smartphone.